In a Wideband Code Division Multiple Access (WCDMA) system, spectrum spreading technologies are adopted to reduce average signal transmission power and Signal to Noise Ratio (SNR) in physical channels, and a gain factor is employed for weighting of transmission signals during the spectrum spreading process to control power usage of the signals.
Signals in a physical channel may be transmitted in a compressed mode or a non-compressed mode. If the signals are transmitted in a non-compressed mode, the gain factor may be provisioned by a Radio Network Controller (RNC) or be computed according to configuration data provisioned by the RNC. If the signals are transmitted in the compressed mode, the gain factor is computed according to gain factor information of the physical channel for different Transport Format Combinations (TFCs) configured in the non-compressed mode and information of the compressed mode. The information of the compressed mode includes parameters such as numbers of pilot bits per slot of the physical channel in the compressed mode and the non-compressed mode, and the number of non DTX slots in a compressed frame.
However, for some uplink physical channels bearing service data, the number of the uplink physical channels may change in the compressed mode. For example, because there is less number of non DTX slots in a compressed frame, the original number of uplink physical channels for the TFC cannot bear the service data in the non-compressed mode. Therefore, the number of the uplink physical channels for the same TFC may change, i.e., may exceed that in the non-compressed mode.
For example, regarding an uplink Dedicated Physical Data Channel (DPDCH), each of DPDCH generally uses the same gain factor. Therefore, if the number of the DPDCHs is n, after weighting of data signals in the DPDCHs and control signals transmitted in an uplink Dedicated Physical Control Channel (DPCCH), a signal power is computed as follows: n×DPDCH gain factor×power of DPDCH+DPCCH gain factor×power of DPCCH; and when the number of the DPDCHs changes from n to n+1, the signal power is computed as follows: (n+1)×DPDCH gain factor×power of DPDCH+DPCCH gain factor×power of DPCCH. The power offset may be relatively high.
As can be seen from the above, the influence brought by the change of the number of physical channels in the compressed mode is not taken into consideration. Therefore, it is not guaranteed that an accurate gain factor is computed and a correction power is acquired in the compressed mode.
Therefore, there is a need for obtaining a correct gain factor in a compressed mode to accurately control the power of the uplink physical channel.